The present invention relates to a receive circuit for a differential serial bus, such as a CAN (xe2x80x9cController Area Network xe2x80x9d) bus system.
A CAN bus is a known simple differential serial bus system which utilizes a known serial communication protocol and which supports distributed real-time control and multiplexing. A CAN bus is capable of operating in noisy electrical environments with a high level of data integrity, and its open architecture and user-definable transmission medium make it extremely flexible. Typical applications of CAN-based networks can be found in automotive and industrial environments. In a particular implementation of a CAN bus system, the bus consists of a four conductor bus which includes a CAN-HI signal conductor, a CAN-LOW signal conductor, a power conductor and a ground conductor. Electronic control units are connected to the bus via transmitter/receiver (transceiverxe2x80x9d) circuits, such as are commercially available from manufacturers such as Philips Semiconductors.
With known commercially available transceivers, certain fault conditions can interfere with the transmission of information over a CAN bus. Such fault conditions would include a signal conductor being shorted to ground or to power, or when either signal conductor is open. It is known to test for such fault conditions by monitoring voltage levels. However, such voltage monitoring may not detect a short to ground fault condition because the voltage resulting from a short to ground condition may lie within the range of the common mode voltage. Accordingly, a differential serial bus receiver which can detect and respond to such fault conditions is desired.
Accordingly, an object of this invention is to provide a system for detecting and overcoming fault conditions in a differential serial bus system.
This and other objects are achieved by the present invention, wherein a receiver circuit is connected to a differential serial bus having first and second signal conductors. The receiver circuit includes a fault detection circuit which generates a difference signal representing a difference between a first signal on the first conductor and a second signal on the second conductors. A comparator/logic circuit includes a plurality of comparators for comparing the difference signal, the first signal and the second signal to predetermined voltage levels. The comparator/logic circuit also includes a plurality of logic units coupled to outputs of the comparators. A signal select circuit has a pair of inputs coupled to the first and second conductors, logic inputs coupled to logic outputs of the comparing circuit, and a signal output. The signal select circuit and the comparing circuit cooperate to control communication of the first and second conductors with the signal output as a function of fault conditions on the first and second conductors.